Flash memories are popular in modern societies. A conventional flash memory is similar to a CMOS (Complementary Metal-Oxide-Semiconductor) transistor, in which the conventional flash memory includes two gates (also called “gate electrodes”) and a spacing film sandwiched between the gates. The spacing film is made of dielectric material and has to electrically isolate both gates from each other to prevent causing a short circuit between the gates, so that the spacing film prefers to have high breakdown voltage. Hence, the spacing film sandwiched between two gates is an important part of the flash memory.